DE69204147T2 - Full catalysts made of chromium and nickel oxides and their use for the fluorination of halogenated hydrocarbons. - Google Patents

Description

The present invention relates to the fluorination of halogenated hydrocarbons by catalysis in the gaseous phase, in particular it relates to novel bulk catalysts based on chromium and nickel and their application to the synthesis of hydrohaloalkanes.

The intensive research currently being carried out into substitutes for fluorocarbons (CFCs) is, among other things, moving in the direction of the synthesis of hydrohaloalkanes. Certain steps of this synthesis can be carried out by heterogeneous catalytic fluorination in the gas phase with hydrogen fluoride.

Numerous metal compounds (e.g. chromium, cobalt, nickel, iron, copper, manganese, etc.) have a catalytic effect on these fluorination reactions. The catalysts proposed in the literature are either bulk catalysts or catalysts applied to a carrier material, whereby the carrier material consists mainly of plastic or aluminum oxide (partially converted to AlF₃ after fluorination).

In this second group, there are a large number of metal compounds and there are many patents describing fluorination based on this type of catalyst. For example, US-A-2 744 147 and US-A-2 744 148 describe the fluorination of a haloalkane over a metal-based catalyst (chromium, cobalt, nickel for US-A-2 744 147 and chromium, cobalt, nickel, copper, palladium for US-A-2 744 148) deposited on alumina.

Recently, there is EP-A-366 797, which describes a fluorination process using a catalyst consisting of at least one metal fluoride (nickel, cobalt, iron, manganese, chromium, copper and silver) deposited on mumini oxide with considerable mesoporosity.

The carrier material gives all of these catalysts a certain degree of solubility. However, since the amount of active mass is lower than in a bulk catalyst, the catalytic activity can be impaired. These low contents of non-precious metals do not allow their economic recovery in the spent catalysts.

Bulk fluorination catalysts are generally based on chromium, and the starting materials for their preparation are very numerous (salts, oxides, halides, etc.).

For example, USA-4 912 270 and EP-A-313 061 claim fluorination processes with catalysts based on chromium oxide, which were obtained by reducing chromium oxide using a alcohol or by pyrolysis of ammonium bichromate.

FR-PS-2 135 473 describes the preparation of a chromium and nickel catalyst and its use for the fluorination of functionally perhalogenated compounds. This catalyst is obtained by thermal decomposition of organic chromium and nickel salts. The remaining nickel content remains low because the Ni/Ni+Cr atomic ratio is always below 0.1.

The publications JP 2-172932/90 and 2-172933/90 describe the fluorination of 1,1-difluoro-1,2,2-trichloroethane (F122) and 1-chloro-2,2,2-trifluoroethane (F 133a) respectively using a chromium catalyst to which a doping metal has been added which allows the reaction temperature to be reduced while maintaining considerable activity and the lifetime of the catalyst is improved by limiting chromium crystallization. Use of chromium together with nickel is not described in the examples of this publication.

FR-PS-2 501 062 describes the production of chromium oxide in bulk in the form of microspheres with a diameter of between 0.1 and 3 mm. This catalyst is obtained by gelling a chromium hydroxysol in a solvent that is immiscible or only partially miscible with water. The product obtained is very stable and is particularly suitable for fluorination reactions in a fluidized bed.

The disadvantage of these chromium oxide-based catalysts is their low resistance to high temperatures (350 - 500ºC) to crystallization, which contributes to reducing their lifespan.

These chromium catalysts also promote the oxidation of hydrogen chloride by the oxygen dissolved in the reagents or deliberately added. The Deacon reaction (Chemical Week 1987, June 24, p. 18) produces water and chlorine, which in turn react with any organic compound, leading to the formation of unusable byproducts and thus to lower selectivity.

It has now been found that the addition of a nickel compound to a chromium derivative to form a hydroxide sol of chromium and nickel, while retaining the advantages of a bulk catalyst, makes it possible not only to extend the life of the catalyst by improving the resistance to crystallization of the chromium compound, but also to improve the selectivity in the fluorination reactions in the gaseous phase thanks to a partial inhibition of the oxidation of hydrochloric acid in the presence of chromium.

The invention thus relates to bulk catalysts based on chromium and nickel oxides, which are formed by a process which essentially consists of:

a) Formation of a hydroxide sol of chromium(III) and nickel(II),

b) gelation of this sol, and

c) Drying and calcining the product to a temperature of between 250 and 450ºC.

The invention also relates to the use of these catalysts for the fluorination of saturated or olefinic halogenated hydrocarbons in the gaseous phase using HF.

In the catalysts according to the invention, which can be in various forms (spheres, extrudates, pellets, etc.), the Ni/Cr atomic ratio can be between 0.05 and 5. Preferably, it is between 0.1 and 3.5, in particular between 0.15 and 3.

Depending on the gelation technique used (in the form of droplets or in bulk), a catalyst precursor is obtained, which is formed from a homogeneous mixture of chromium and nickel hydroxides, which, after drying, are in the form of either microspheres or powder, the powder being shaped according to conventional methods, for example by extrusion or by substrate formation. After calcination, a bulk catalyst is obtained, formed from a homogeneous mixture of chromium and nickel oxides.

The chromium(III) and nickel(II) hydroxide sol can be formed in a known manner from the chromium and nickel precursors.

Chromium precursors include oxides, hydroxides, halides, oxyhalides, nitrates, acetates and sulfates of chromium, but any other chromium compound suitable for forming a chromium hydroxide sol can also be used. The preferred precursors are the chromium salts, such as sulfates, chlorides, acetates and nitrates; chromium (III) sulfate or acetate is particularly preferred.

Nickel precursors include the hydroxides, oxyhalides, nitrates, acetates and sulfates of this metal, but any other nickel compound that is soluble in water and allows the formation of a sol or that can be introduced into the gel formed from chromium can also be used. The preferred precursors are the very water-soluble salts, such as nitrates, especially nickel chlorides or sulfates.

For certain chromium and nickel boron stages, in particular the oxides, hydroxides, acetates and sulphates, the sol can form at ambient temperature. On the other hand, the formation of the sol requires a heating step to a temperature between 60 and 100ºC, preferably between 80 and 95ºC, if the precursor is a chromium nitrate or halide. On the other hand, it is advantageous to heat the solution of the precursors to a temperature between 60 and 100ºC, preferably between 80 and 95ºC, even if the precursors allow the formation of a sol at low temperature.

Furthermore, the formation of the sol can be completed by adding to the aqueous solution of the precursors a complexing agent for chromium and/or nickel, for example ammonium acetate, sulphate or phosphate, in a molar amount which can be up to 5 times the total number of moles of chromium and nickel precursors.

Various additives can be added to the sol to improve the physicochemical and catalytic properties of the catalyst obtained. The following can be added (in %, based on the weight of the sol):

a) 2 to 10% Cr₂O₃ or Cr₂O₃ 2H₂O powder previously dried at 300°C to improve the mechanical cohesion of the microspheres;

b) 01 to 3% alumina monohydrate to increase the resistance to wear of the catalyst;

(c) 5 to 25% hexamethylenetetramine and/or urea, the presence of which leads to decomposition at gelling temperatures of the gel with additional release of ammonia;

d) 1 to 10% colloidal silica to improve the porosity of the catalyst (the silica is removed during treatment with hydrogen fluoride in the form of silicon tetrafluoride);

e) other additives, such as wetting agents (e.g. lauryl diethanolamide, polyethylene glycol monostearate) or thickeners (e.g. hydroxymethylcellulose, microcrystalline cellulose) to improve the sphericity of the microspheres.

The mixed catalysts of chromium and nickel oxides formed according to the invention starting from a chromium and nickel hydroxide sol can be obtained in the form of microspheres by gelling the sol in the following manner:

1. Dispersion of the sol in the form of droplets in an organic solvent that is immiscible or only partially miscible with water and gelling at elevated temperature;

2. Incorporation of the formed microspheres in the gelling solvent or in an ammoniacal solution to complete gelation;

3. Wash the microspheres with diluted ammonia water and with water to remove impurities and dry if necessary.

First step

The formation and gelation of the microspheres is carried out in a column with a height between 1 and 6 m, extended by a release zone, through which a hot solvent passes from bottom to top.

The chromium and nickel hydroxide sol is introduced at the top of the column by means of a small diameter tube, this tube being arranged concentrically inside another tube of larger diameter through which the solvent cooled to a temperature of not more than 30ºC (preferably 25ºC) is introduced in cocurrent to avoid gel formation in the inlet tubes.

The diameter of the inlet tube and the flow rate of the sol determine the dispersions of the droplets and thus the final size of the microspheres.

During the injection, it is advisable to maintain the sol at a temperature between 3 and 8ºC, preferably between 3 and 5ºC, in order to avoid variations in its viscosity. These variations are expressed by an evolution of the sol and therefore of the physicochemical properties of the microspheres.

It is advantageous to partially neutralize the sol before its introduction with a sufficient quantity of ammonia in order to obtain a viscosity adapted to the dispersion of the beads. This quantity depends on the nature of the chromium and nickel precursors used; the NH4OH/Cr+Ni molar ratio is preferably less than 2, in particular less than 1.5.

The rising stream of hot solvent (temperature between 25 and 41ºC) is added at the bottom of the column at a rate of rise between 0.1 and 5 m/s. This Speed determines the residence time of the microspheres and thus their degree of gelation.

In the upper part of the column there may be a second feed for the solvent cooled to a temperature of not more than 30ºC. This facilitates the maintenance of a temperature gradient in the column and enables the control of the gelation rate.

The organic solvent that is not or only partially miscible with water can be selected from alcohols such as butanol, hexanol, 2-ethylpentanol, 2-ethylhexanol, with the last alcohol being preferred.

Second step

At the bottom outlet of the column, the microspheres are placed in a receiver containing the organic gelling solvent or, preferably, the ammoniacal solution, the concentration of which is between 0.1 and 14 N and the temperature of which is maintained between 15 and 70 °C, preferably between 25 and 50 °C.

The presence of ammonia in the containment device increases the gelling efficiency of the microspheres, thereby increasing their mechanical cohesion and ensuring a first washing process. Increasing the concentration of the ammoniacal solution allows an increase in the strength and density of the microspheres.

Third step

The microspheres are washed several times with dilute ammonia water (0.1 to 1 N), then washed with water before being dried, if necessary, in air at a temperature between approximately 80 and 200ºC. This drying at low However, temperature can be omitted without the risk of a change in the properties of the microspheres.

The microspheres are then calcined under inert gas (e.g. nitrogen, argon, etc.) or under air at a temperature between 250 and 450ºC, preferably between 300 and 420ºC.

Instead of being gelled in the form of microspheres according to the method described above, the chromium and nickel hydroxide sol can be completely gelled by adding a base, preferably ammonia, until the hydroxide sol caking. The product thus obtained is then washed with dilute ammonia water (0.1 to 1 N) and/or water before being dried at a temperature of between 80 and 200°C. The washing and filtration operations can be facilitated by adding 5 to 100 ppm of a flocculant, preferably polyacrylamide. The catalyst is then calcined as described above; this calcination can be preceded or followed by shaping according to known techniques (extrusions, pre-pressing).

The catalysts according to the invention in bulk can be used for the fluorination of saturated or olefinic halogenated hydrocarbons in the gaseous phase by means of HF. They are particularly suitable for the fluorination of halogenated hydrocarbons which lead to fluorinated C₁ to C₃ compounds with one or more hydrogen atoms. Examples of halogenated hydrocarbons as starting compound include, by way of non-limiting example, the following compounds: CHCl₃, CCl₂=CHCl, CHCl₂-CClF₂, CH₂Cl-CF₃, CH₃-CCl₂-CH₃, CCl₃-CF₂-CH₃, CCl₃-CF₂-CHCl₂, CCl₃-CF₂-CH₂Cl, CHCl₂-CHCl-CH₃, CH₂Cl-CHCl-CH₃ and also CCl₂=CCl₂; this last compound does not contain a hydrogen atom, but the addition of HF leads to hydrohalogenated compounds.

To work with optimal activity, it is necessary to subject the catalyst to a treatment with hydrogen fluoride diluted or not with nitrogen. Although the presence of nickel delays the crystallization of the catalyst, such activation can locally cause temperatures above 500ºC. It is therefore advisable to control the heat release of the activation by varying the addition of the HF diluent and by starting this treatment at a low temperature (150-200ºC). On the other hand, after the "energy release development" in the catalytic bed, it is advisable to gradually increase the temperature to reach a maximum of 350 to 450ºC at the end of the activation.

The reaction temperature of the fluorination depends on the reaction being studied and, of course, on the desired reaction products. Thus, for the partial substitution of chlorine atoms by fluorine, temperatures between approximately 50 and 350ºC are used; the total substitution of the chlorine atoms may require temperatures between 300 and 500ºC

The contact times also depend on the reaction studied and the desired products. In general, they are between 3 and 100 seconds; however, these contact times generally remain below 30 seconds in order to achieve a good compromise between the degree of conversion and increased productivity.

The molar ratio between HF and organic compound is also linked to the reaction being studied: it depends, among other things, on the stoichiometric nature of the reaction. In most cases it can be between 1/1 and 20/1, but even then it is often below 10 in order to achieve increased productivity.

The working pressure is preferably between 1 and 20 bar absolute (0.1 to 2 MPa).

The catalysts according to the invention can be used in a fixed bed or in a fluidized bed. The catalysts in the form of microspheres are very durable and therefore particularly suitable for reactions in a fluidized bed.

Catalysts whose activity has decreased as a result of contamination can be regenerated by flushing the catalyst with a compound that enables the oxidation and transformation of the products (organic products, coke, etc.) that have deposited on the catalyst as volatile products. Oxygen or a mixture containing oxygen (e.g. air) is ideal for this purpose and enables the catalyst to regain its initial activity.

To ensure regeneration of the catalyst without crystallization, it is recommended to carry out this treatment at a temperature between 200 and 450ºC, and in particular between 300 and 380ºC. It is also advisable to limit the energy released by this "combustion" by controlling the oxygen flow (at the start of the regeneration, a low oxygen flow diluted with an inert gas), while keeping the temperature below 450ºC.

In order to maintain the catalyst activity, it is equally possible to carry out the fluorination reaction in the presence of oxygen, which can be added in a molar ratio of O₂ to the organic compound of 0.001 to 0.05, preferably between 0.005 and 0.03.

The following examples serve to illustrate the invention without limiting it. The pore volume given in Examples 1 to 12 was determined by mercury porosimetry and corresponds to a pore radius between 4 nm and 63 µm.

PRODUCTION OF CATALYSTS Example 1: Catalyst A

The procedure is carried out in a device as shown in the figure, which essentially consists of the following parts:

- a glass reactor (1) with a volume of 3 litres for producing the chromium and nickel hydroxide sol; this is double-jacketed and equipped with a biconical stirring device (11) at 3000 rpm; a pump and a heat exchanger (12) allow a reduction in the heat of neutralisation and thus the maintenance of the desired sol temperature;

- a glass column (2) for gelling the sol in the form of microspheres; this column (80 mm diameter and 1.5 m high) is extended at the top by a release zone (21) of 100 mm diameter and 100 mm high;

- an introduction device (3) consisting of a tube with an internal diameter of 2 mm for introducing the sol into column 2; this tube is arranged concentrically inside a tube with an internal diameter of 12 mm through which 2-ethylhexanol is introduced;

- a collecting tank (4) for collecting the microspheres formed in column 2; this tank has a volume of 5 litres and contains the homogenised ammonia water and is maintained at the desired temperature by a circuit consisting of a pump and a heat exchanger (41);

- a tank (5) for feeding the input device 3 and the column 2 for 2-ethylhexanol, which serves as a dehydration solvent.

a) Preparation of a chromium and nickel hydroxide sol

Prepare an aqueous solution of chromium and nickel at ambient temperature by dissolving 550 g of basic chromium sulfate Cr2(SO4)2(OH)2Na2SO4 and 238 g of nickel chloride hexahydrate NiCl2H2O in 367 g of water. Add 70 g of crystalline chromium(III) oxide to this aqueous solution.

The mixture is cooled to 5ºC and, while maintaining this temperature, the following are added in succession:

- 151.5 g cold 11N ammonia solution (5ºC)

- a cold aqueous solution (5ºC) of 204 g hexamethylenetetramine, 10.8 g urea and 300 ml water

- 225 g of a 30% silicon dioxide sol in water (CECASOL from CECA).

b) Introduction of the sol and preparation of the microspheres

The chromium and nickel hydroxide sol prepared according to step a) is then introduced into the column 2 through the line (13) using a pump (14). The use of a peristaltic pump allows any flow rate fluctuations to be avoided. For longer lengths of the feed line 13, it is necessary to sheath it in order to avoid cold losses.

The sol at 5ºC is introduced at a rate of 0.6 l/h through the tube with an internal diameter of 2 mm, while 2-ethylhexanol at a temperature of 25ºC is introduced through the line 51 at a rate of 10 l/h through the tube with an internal diameter of 12 mm in order to prevent premature gelling of the sol in the introduction device 3; the end of the last tube is immersed in the organic solvent by approximately 5 mm. A flow of 2-ethylhexanol at the same temperature (25ºC) can be introduced into the upper part of the column through the feed line 52, the outlet of which is located below the release zone.

A further feed of 2-ethylhexanol heated to a temperature of 120º is introduced into the lower part of the column via feed line 53 at a flow rate of 45 l/h. This 2-ethylhexanol stream passes through the column from bottom to top at a rising flow rate of approximately 9 m/h and is discharged through an overflow pipe in the upper release zone. The two 2-ethylhexanol streams allow a temperature gradient to be created in the column, which is necessary to control the kinetics of gelation and dehydration of the sol.

The 2-ethylhexanol discharged from the column is fed through line 54 into tank 5. In a device not shown in the figure, it is previously purified by washing with water and distillation to remove dissolved ammonium sulfate, organic residues (urea, hexamethylenetetramine, formaldehyde) and water extracted from the sol.

At the bottom of the column, the micro-particles are collected in a collecting tank 4 containing homogenized 1 N ammonia water, which is kept at 90ºC by the closed circuit 41.

Production is approximately 100 g/h per injector, but this can be increased by using multiple injectors.

The microspheres are washed extensively with dilute ammoniacal solution (0.1 N), then with water and dried at 120ºC. They are then calcined at 420ºC under a nitrogen atmosphere for 4 hours.

The catalyst A thus obtained has the following properties:

- Ni/Cr atomic ratio = 0.34

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.25 g/cm³

specific surface area (BET) = 185 m²/g

- Pore volume (mercury porosimetry) = 0.05 cm³/g (4 nm < rpores < 63 um)

- Compressive strength in bed (BCS) = 0.21 MPa

Example 2: Catalyst B

The procedure is as in Example 1, but an ammoniacal solution of 11 N is used in the microsphere collection tray instead of 1 N.

The properties of the catalyst B thus obtained are as follows:

- Ni/Cr atomic ratio = 0.27

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.4 g/cm³

- specific surface area (BET) = 102 m²/g

- Pore volume = 0.07 cm³/g

- Compressive strength in bed (BCS) = 0.74 MPa

Example 3: Catalyst C

The procedure is as in Example 1, but without adding silicon dioxide sol. A catalyst C with the following properties is obtained:

- Ni/Cr atomic ratio = 0.25

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.5 g/cm³

- specific surface area (BET) = 25 m²/g.

- Pore volume = 0.09 cm³/g

Example 4: Catalyst D

The procedure is as in Example 1, reducing the nickel content, i.e. starting from an aqueous solution by dissolving 550 g of basic chromium sulfate and 45 g of nickel chloride hexahydrate in 440 g of water.

The catalyst D thus obtained has the following properties:

- Ni/Gr atomic ratio = 0.07

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1> 38 g/cm³

- specific surface area (BET) = 187 m²/g

- Pore volume = 0.044 cm³/g

Example 5: Catalyst E

The procedure is as in Example 1, but the microspheres are calcined at 350ºC instead of 420ºC. The catalyst E thus obtained has the following properties:

- Ni/Cr atomic ratio = 0.37

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.1 g/cm³

- specific surface area (BET) = 178 m²/g

- Pore volume = 0.09 cm³/g

Example 6: Catalyst F (comparative example)

The procedure is as in Example 1, but no nickel is used. The aqueous starting solution consists only of basic chromium sulfate (550 g) and water (475 g).

The properties of this catalyst F, prepared as a comparative example, are as follows:

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.04 g/cm³

- specific surface area (BET) = 209 m²/g

- Pore volume = 0.052 cm³/g

- Compressive strength in bed (BCS) = 0.37 MPa

By replacing the ammonia present in the receiving tank with 2-ethylhexanol at 120ºC, by modifying the device as shown in the attached Figure 2, a product with the following properties is obtained:

- Bulk density = 1.07 g/cm³

- specific surface area = 203 m²/g

- Bed pressure resistance (BCS) = 0.23 MPa

Example 7: Catalyst G (comparative example)

The procedure is as in Example 6, but the microspheres are calcined at 350ºC instead of 420ºC.

The catalyst thus obtained has the following properties:

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.3 g/cm³

- specific surface area (BET) = 181 m²/g

- Pore volume = 0.05 cm³/g

Example 8: Catalyst H (comparative example)

The procedure is as in Example 1, but neither nickel nor silicon dioxide sol is added. The aqueous starting solution is formed only from basic chromium sulfate (550 g) and water (475 g).

The properties of the catalyst H prepared as a comparative example are as follows:

- Diameter of microspheres = 0.5 to 2.5 mm

- Bulk density = 1.4 g/cm³

- specific surface area (BET) = 10 m²/g

- Pore volume = 0.28 cm³/g

Example 9: Catalyst I

A solution of 200 g of non-hydrated chromium nitrate and 118.8 g of nickel chloride hexahydrate in 1000 g of water is prepared. This solution is heated to 80ºC for 2 hours and, after cooling to 20ºC, is gelled by adding 190 ml of 14.7 N ammoniacal solution.

The gel is then washed twice with 450 ml of 0.1 N ammonia water, then twice with distilled water, each washing process is followed by filtration.

The powder obtained is then dried for 14 hours at 100ºC under vacuum (20 kPa), then calcined at 350ºC under nitrogen atmosphere for 4 hours.

The properties of the catalyst I thus obtained are as follows:

- specific surface area (BET) = 160 m²/g

- Pore volume = 0.74 cm³/g

Example 10: Catalyst J (comparative example)

Proceed as in Example 9, but heat the solution of chromium and nickel salts to 40ºC instead of 80ºC.

The catalyst J thus obtained has the following properties:

- specific surface area (BET) = 139 m²/g

- Pore volume = 0.60 cm³/g

Example 11: Catalyst K

Prepare an aqueous chromium and nickel solution by dissolving 274 g of nickel chloride hexahydrate in 200 g of water and then adding 275 g of basic chromium sulfate and 183.5 g of water.

To this solution, 112 g of CECASOL are added, then 390 ml of a 11 N ammoniacal solution until the sol has completely cured. The gel obtained is washed with a dilute ammoniacal solution and water before being dried at 120ºC for 15 hours and calcined at 250ºC for 4 hours.

The powder obtained is added to an aqueous 12% polyvinyl alcohol solution, then dried at 85ºC for 15 hours. The mixture is then shaped by substrate formation and calcined at 420ºC for 4 hours. The catalyst K thus obtained has the following properties:

Cr = 24.7% by mass

Ni = 20.15% by mass

Ni/Cr atomic ratio = 0.42

specific surface area (BET) = 54.8 m²/g

Pore volume = 0.162 cm³/g

Example 12: Catalyst L (comparative example)

A chromium and nickel solution is prepared by mixing at ambient temperature 80 ml of a 1 M solution of Cr(NO3)3 9H2O and 80 ml of a 1 M solution of NiCl2 6H2O. This mixture is then neutralized with 50 ml of a 14 N ammoniacal solution and the product obtained by centrifugation is dried at 100°C for 15 hours.

The powder obtained is added to 0.4 g of graphite and 5.1 g of an aqueous 12% polyvinyl alcohol solution, then dried at 100°C (15 hours) and shaped into a substrate. The product obtained is calcined at 350°C for 4 hours.

The catalyst L has the following properties:

Ni/Cr atomic ratio = 0.95

specific surface area (BET) = 82.8 m²/g

Pore volume = 0.17 cm³/g

Fluorination examples

In the following examples:

- the percentages are mole percent;

- the hydrogen fluoride used is a commercially available product containing only traces of water;

- the starting product 1-chloro-2,2,2-trifluoroethane (F 133a) is a product with a purity of 99.9%;

- the reactor used is a 250 ml Inconel tube heated by means of an alumina flow bath.

The activation of the catalyst with HF is carried out in this reactor with a 100 ml sample. After drying under nitrogen (5 l/h) at 250ºC for 3 hours, the hydrogen fluoride is gradually added to the nitrogen at this same temperature for a period of 5 hours (2 moles of HF are added over 5 hours). After passing through the exothermic peaks, the HF flow rate is increased until 1 mole/h is reached, then the temperature is raised to 350ºC. A temperature gradient is observed under these conditions for 8 hours.

After being introduced into the reactor, the reagents are mixed and heated to the reaction temperature in an Inconel preheater.

After washing with water - to remove the hydrogen acids - and drying over CaCl2, the reaction products are analyzed one by one by gas chromatography.

Examples 13 to 15

The fluorination tests are carried out with F 133a at atmospheric pressure in the absence of oxygen using catalysts A, D and F activated according to the procedures described previously. The fluorination results are given in Table 1.

It is observed that the activity of catalyst F (chromium only) decreases much faster than that of catalysts A and D (nickel-chromium) and that the selectivities are also less good. TABLE 1 Catalyst Example Comparative Example Catalyst Age (hours) Molar Ratio Contact Times Temperature (ºC) Conversion Degree of Selectivity

Examples 16 and 17

Fluorination tests are carried out on F 133a under an absolute pressure of 1.5 MPa in the presence of oxygen by bubbling air with catalysts E and G activated according to the procedure described above. The fluorination results are given in Table 2. TABLE 2 Catalyst Example Comparative Example Catalyst Age (hours) Molar Ratio Contact Times Temperature (ºC) Conversion Degree of Selectivity

As previously stated, catalyst E (Ni-Cr) (Example 16) gives a more stable activity and a better selectivity than catalyst G without nickel (Example 17).

Examples 18, 19 and 20

These examples, given in Table 3 below, were carried out with catalysts C and H without silica and allow a comparison of the results of the fluorination of F 133a under atmospheric pressure in the absence of oxygen.

After 548 hours of use, the catalyst C from Example 19 is subjected to regeneration by treatment with air (1 mol/h) at 300ºC for 24 hours. The catalyst C thus regenerated is subsequently used for the tests of Example 20.

The study of the results allows to evaluate the effect of nickel on the activity of the catalyst despite the absence of silica.

It is also observed that the regenerated catalyst C (Example 20) has an activity comparable to that of catalyst C at the beginning of the experiment. TABLE 3 Catalyst Comparative Example Example regenerated Catalyst age (hours) Molar ratio Contact times Temperature (ºC) Conversion rate of Selectivity (*) After regeneration

Example 21

This example, given in Table 4 below, was carried out at atmospheric pressure in the absence of oxygen using catalysts I and J prepared from the sol heated to 80 and 40 ºC respectively. TABLE 4 Catalyst J (comparative) Catalyst age (hours) Molar ratio Contact times Temperature (ºC) Conversion rate of Selectivity

The study of the results allows an evaluation of the influence of the preparation temperature of the chromium and nickel sol on the activity of the catalyst.

Claims (13)

1. Full catalysts based on chromium and nickel oxides, characterized in that the atomic ratio of nickel to chromium is 0.05 to 5 and the catalysts are produced by a process that essentially consists of the following steps: a) Formation of a sol of chromium(III) and nickel(II) hydroxides, b) gelation of the sol, and c) Drying and calcining the product at a temperature between 250 and 450ºC. 2. Catalysts according to claim 1, wherein the atomic ratio of nickel to chromium is between 0.1 and 3.5, preferably between 0.15 and 3 . 3. Catalysts according to claim 1 or 2, characterized in that the chromium and nickel hydroxide sol is obtained from chromium (III) sulfate, acetate or nitrate and from nickel chloride, sulfate or nitrate. 4. Catalysts according to one of claims 1 to 3, characterized in that the sol additionally contains at least one additive, selected from: - powder of crystallized Cr₂O₃, - Aluminium oxide monohydrate, - hexamethylenetetramine and/or urea, - colloidal silicon dioxide - wetting agents, - thickeners. 5. Catalysts according to one of claims 1 to 4, characterized in that the formation of the sol comprises a heating step to a temperature between 60 and 100 °C, preferably between 80 and 95 °C. 6. Catalyst according to one of claims 1 to 5, characterized in that the sol is formed in the presence of a chromium and/or nickel complexing agent. 7. Catalyst according to one of claims 1 to 6, characterized in that the sol is gelled by means of ammonia. 8. Catalyst according to one of claims 1 to 7, in the form of microspheres, characterized in that the gelation of the sol of chromium and nickel hydroxides is carried out in the following way: (a) dispersion of the sol in the form of small droplets in an organic solvent which is immiscible or slightly miscible with water and gelation at elevated temperature; (b) taking up the formed microspheres in the same organic solvent or in an ammoniacal solution; (c) Washing the microspheres with dilute ammonia, then with water, optionally followed by drying. 9. Catalyst according to claim 8, characterized in that the organic solvent is 2-ethylhexanol. 10. Catalyst according to one of claims 1 to 7, characterized in that it is in the form of pellets or extrudates. 11. Catalyst according to one of claims 1 to 10, characterized in that the calcination is carried out at a temperature between 300 and 420°C. 12. Process for the fluorination of saturated or olefinic halogenated hydrocarbons with HF in the gas phase, characterized in that a catalyst according to one of claims 1 to 11 is used. 13. The process of claim 12, wherein the halogenated hydrocarbon is 1-chloro-2,2,2-trifluoroethane.